Exposure mask, method of designing and manufacturing the same, exposure method and apparatus, pattern forming method, and device manufacturing method

ABSTRACT

A method of designing an exposure mask for exposing an image forming layer provided on a substrate, by use of near field light leaking from adjoining openings formed in a light blocking member. The method includes determining a width D of the openings and an opening interval of the openings to be formed in the light blocking member, in which a relation D≦(P−W−2T) is satisfied where T is the height of a pattern to be produced by the image forming layer, W is the linewidth of the pattern and P is the pitch of the pattern, so that an electrical field distribution, adjacent to the opening of the light blocking member as exposure light is projected on the light blocking member, is approximated to an electrical field model extending concentric-circularly with an edge of the light blocking member at an image forming layer side as a center.

This application claims priority from Japanese Patent Application No.2003-182041, filed Jun. 26, 2003, and Japanese Patent Application No.2004-097699, filed Mar. 30, 2004, which are hereby incorporated byreference herein.

TECHNICAL FIELD

This invention relates generally to near field exposure technology thatenables the production of a fine pattern and, more particularly, to anexposure mask, a method of designing and manufacturing an exposure mask,an exposure method and apparatus, a pattern forming method, and a devicemanufacturing method, for example.

BACKGROUND ART

Increasing capacity of a semiconductor memory and increasing speed anddensity of a CPU processor have inevitably necessitated furtherimprovements in fineness of microprocessing through optical lithography.Generally, the limit of microprocessing with an optical lithographicapparatus is on an order of the wavelength of light used. Thus, thewavelength of light used in optical lithographic apparatuses has beenshortened more and more. Currently, a near ultraviolet laser is used,and microprocessing on the 0.1 μm order is enabled. While the finenessis being improved in the optical lithography, in order to assuremicroprocessing of 0.1 μm or narrower, there still remain many unsolvedproblems, such as further shortening of laser wavelengths, developmentof lenses usable in such a wavelength region, and the like.

On the other hand, as a measure for enabling microprocessing of 0.1 μmorder or narrower, a microprocessing apparatus using a structure of anear-field optical microscope (scanning near-field optical microscope:SNOM), has been proposed. An example is an exposure apparatus in which,by use of evanescent light leaking from a fine opening of a size notgreater than 100 nm, local exposure that exceeds the light wavelengthlimit is performed to a resist.

However, since such a lithographic apparatus with an SNOM structure isarranged to execute the microprocessing by use of one or more processingprobes, as in continuous drawing there is a problem that the throughputis not high.

As one method for solving such a problem, U.S. Pat. No. 6,171,730proposes an exposure method in which a photomask, having a patternarranged so that near field light leaks from a light blocking film, isclosely contacted to a photoresist upon a substrate, whereby a finepattern of the photomask is transferred to the photoresist at once.

The method and apparatus disclosed in the aforementioned U.S. patent isvery useful and it makes a large contribution to the technical field towhich the present invention pertains.

Also, Japanese Laid-Open Patent Application No. 11-317345 and U.S. Pat.No. 6,497,996 disclose that such near field light has a property thatthe intensity is attenuated as with an exponential function, with thedistance from the fine opening, and, thus, the film thickness of apattern forming layer based on the near field exposure has to be madethin.

FIG. 2 illustrates a near-field electrical field distribution around amask opening obtained by investigation made through simulations.Specifically, FIG. 2 shows the state of an electrical field distributionproduced adjacent to the opening, where light having a wavelength of 436nm is projected to a near-field exposure mask having a pitch of 200 nmand a mask opening width of 70 nm. Values in the drawing are relativeelectrical field intensities at respective positions where the intensityof incident light is taken as one.

Seeing the electrical field distribution, there is an extension from theopening to the light blocking film portion. This means that there is apossibility that the opening pattern of the mask and the patternprovided by exposure do not completely correspond to each other.

The feature that the electrical field intensity attenuates as comingaway from the mask opening and that there appears an electrical fielddistribution being extended in a direction parallel to the mask surface,such as depicted in FIG. 2, is peculiar to the near field.

Generally, making an exposure mask takes a very long time and isexpensive. In the mask pattern production for near field exposure,particularly, the mask design should be done while taking into accountthis electrical field distribution.

On the other hand, as the pattern width to be produced becomes narrower,the mask design should be made while more exactly taking into accountthe extension described above.

However, if the mask opening width having an electrical fielddistribution that can meet various pattern linewidths and pitches issought through complicated simulations using many varieties ofparameters, it takes a long time to complete the simulation andanalysis. Consequently, it causes a problem that the mask designing alsorequires a long time.

DISCLOSURE OF THE INVENTION

It is accordingly an object of the present invention to provide anexposure mask, an exposure mask designing and manufacturing method, anexposure method and apparatus, a pattern forming method and/or a devicemanufacturing method, by which at least one of the inconveniencesdescribed above can be solved, and by which a mask structure can beaccomplished easily while taking into account the electrical fielddistribution peculiar to the near field, without the necessity ofcomplicated simulation, which requires a long time.

The present invention can provide an exposure mask, an exposure maskdesigning and manufacturing method, an exposure method and apparatus, apattern forming method and a device manufacturing method, which may takethe following forms, for example:

(1) An exposure mask for exposing an image forming layer provided on asubstrate, by use of near field light leaking from adjoining openingsformed in a light blocking member, characterized in that the lightblocking film has an opening interval that is determined so that anelectrical field distribution at the image forming layer side of theopening, to be defined as exposure light, is projected on the lightblocking member and has a correlation with an eccentric model of anelectrical field distribution as determined by a linewidth and a heightof a pattern to be produced.

(2) An exposure mask for exposing an image forming layer provided on asubstrate, by use of near field light leaking from adjoining openingsformed in a light blocking member, characterized in that a relationK≧(W+2T) is satisfied, where T is the height of a pattern to be producedby use of the image forming layer, W is the linewidth of the pattern,and K is the width of the light blocking member being present betweenadjacent openings.

(3) An exposure mask for exposing an image forming layer provided on asubstrate, by use of near field light leaking from adjoining openingsformed in a light blocking member, characterized in that a relationD≦(P−W−2T) is satisfied, where T is the height of a pattern to beproduced by use of the image forming layer, W is the linewidth of thepattern, P is the pitch of the pattern, and D is the width of theopening.

(4) An exposure mask for exposing an image forming layer provided on asubstrate, by use of near field light leaking from adjoining openingsformed in a light blocking member, characterized in that a relationD={P−W−2T(1+α)} is substantially satisfied where T is the height of apattern to be produced by use of the image forming layer, W is thelinewidth of the pattern, P is the pitch of the pattern, and D is thewidth of the opening, while taking into account a process margin α afterthe exposure.

(5) An exposure mask as mentioned in item (3) or (4) above, wherein thevalue of the pitch is made not greater than the wavelength of a surfaceplasmon polariton wave to be produced on the basis of the light blockingmember.

(6) An exposure mask as mentioned in any one of items (1) to (5),wherein the openings of the mask have a two-dimensional shape or theyare arranged two-dimensionally, with respect to a direction along thesurface of the light blocking member where the openings are formed.

(7) A method of designing an exposure mask for exposing an image forminglayer provided on a substrate, by use of near field light leaking fromadjoining openings formed in a light blocking member, characterized inthat: an opening interval of the light blocking film is determined onthe basis of a linewidth and a height of a pattern to be produced by useof the image forming layer.

(8) A method of manufacturing an exposure mask for exposing an imageforming layer provided on a substrate, by use of near field lightleaking from adjoining openings formed in a light blocking member,characterized in that an opening interval of the light blocking film isdetermined on the basis of a linewidth and a height of a pattern to beproduced by use of the image forming layer, and that, the light blockingmember is subsequently processed so as to obtain the thus determinedopening interval.

(9) An exposure method for exposing an image forming layer provided on asubstrate, by use of an exposure mask having a light blocking memberwith an opening and on the basis of near field light leaking from theopening, characterized by a step of preparing an exposure mask as in anyone of items (1) to (6), a step of approximating the near-field exposuremask and the image forming layer to each other, up to a distance notgreater than a near field region, and an exposure step for irradiatingthe image forming layer with exposure light through the exposure mask.

(10) An exposure method as mentioned in item (9), wherein, when P is thepitch of a pattern to be produced by use of the image forming layer, Dis the width of the opening, W′ is the linewidth, and T′ is the patternheight, through adjustment of an exposure amount in the exposure stepand of another condition or conditions, exposure is carried out tosatisfy a relation (W′+2T′)≦(P−D).

(11) A pattern forming method including an exposure step for exposing animage forming layer on the basis of near field light and by use of anear-field exposure mask having a light blocking member with openingshaving a pitch P and an opening width D, and a developing step fordeveloping the exposed image forming layer, characterized in thatthrough adjustment of an exposure amount in the exposure step and adeveloping condition in the developing step, a pattern having alinewidth W and a height T satisfying a relation (W+2T)≦(P−D) isproduced.

(12) A method as in item (11), wherein, when a minimum value of theheight T of the pattern is determined as T″ due to a process after thepattern formation, a pattern having a linewidth W that satisfies arelation W<(P−D−2T″) is produced.

(13) A device manufacturing method characterized by including anexposure step for exposing a process object by use of an exposure methodas in item (9), and a developing step for developing the exposed processobject, wherein, after these steps, a predetermined process is conductedto the process object, whereby a device is manufactured.

(14) An exposure apparatus, including light irradiating means and anexposure mask, for exposing a process object provided on a substrate, byuse of near field light leaking from a plurality of openings formed in alight blocking member of the mask, characterized in that as the exposuremask, the exposure apparatus comprises an exposure mask as in any one ofitems (1) to (6).

In accordance with the present invention, it is possible to accomplishan exposure mask, an exposure mask designing and manufacturing method,an exposure method and apparatus, a pattern forming method and/or adevice manufacturing method, by which a mask structure can beaccomplished easily, while taking into account the electrical fielddistribution peculiar to the near field, without the necessity of acomplicated simulation that requires a long time. Therefore, design andproduction of a near-field exposure mask can be achieved efficiently.Particularly, in the production of a desired fine pattern not greaterthan the wavelength of light used for the exposure, the throughput canbe improved significantly and, thus, the cost can be decreased well.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view for explaining the present invention and,specifically, it illustrates how to determine an opening width of anear-field exposure mask on the basis of a concentric-circle model.

FIG. 2 is a schematic view for explaining the present invention and,specifically, it illustrates a simulation result that shows anelectrical field intensity produced adjacent to the openings.

FIG. 3 is a schematic view for explaining the present invention and,specifically, it illustrates a simulation result that shows anelectrical field intensity produced adjacent to the openings, as well asa concentric-circle model.

FIG. 4 is a schematic view for explaining how to determine an openingwidth of a near-field exposure mask on the basis of a concentric-circlemodel, in accordance with an embodiment of the present invention.

FIG. 5 is a schematic view of a general structure of a near-fieldexposure mask according to an embodiment of the present invention.

FIG. 6 is a sectional view showing a general structure of a near-fieldexposure apparatus according to an embodiment of the present invention.

FIG. 7 is a graph illustrating a solubility curve of a certain resist.

FIG. 8 is a schematic view for explaining a pattern width W′ producedthrough near field exposure in accordance with an embodiment of thepresent invention.

FIGS. 9A-9C′ illustrate examples of resist patterns which are obtainablefrom masks having a two-dimensional shape pattern, wherein FIGS. 9A and9A′ are a case where a mask pattern having grid-like fine openings isused, wherein FIGS. 9B and 9B′ are a case where a mask having atwo-dimensional fine opening array is used, and wherein FIGS. 9C and 9C′are a case wherein a mask, whose light blocking metal film has atwo-dimensional rectangular array, is used.

FIGS. 10A and 10B illustrate a resist pattern obtainable when a maskhaving a two-dimensional shape pattern is used, and specifically, FIG.10A shows a resist pattern obtainable when a mask that has a lightblocking metal film having a ring-like shaped is used.

FIG. 11 is a schematic view for explaining the present invention and,specifically, it illustrates how to determine a minimum value of anopening interval of a near-field exposure mask in accordance with aconcentric-circle model.

BEST MODE FOR PRACTICING THE INVENTION

In accordance with one aspect, the present invention provides anexposure mask, an exposure mask designing and manufacturing method, anexposure method and apparatus, a pattern forming method and/or a devicemanufacturing method, by which a mask structure can be accomplishedeasily while taking into account the electrical field distributionpeculiar to the near field, without the necessity of a complicatedsimulation that requires a long time. This is based on the followingfindings acquired by the inventors of the present invention.

Namely, in the mask designing taking into account the extension peculiarto the near field, from simulations, it has been found that theelectrical field distribution adjacent to the opening of a mask fromwhich near field light emits takes the form of an electrical fielddistribution having an approximately concentric extension. Also, it hasbeen found that such an electrical field distribution can beapproximated by a concentric-circle model, and that, by using such aconcentric-circle model and from the pattern width W and pattern heightT (pitch P in the case of a periodic pattern), the structure of anear-field exposure mask to be prepared can be determined easily byequations, without the necessity of simulations.

This will be explained in greater detail.

FIG. 2 shows a near-field electrical field distribution produced nearfine openings. This is the result of a simulation made by the use of akind of GMT (Generalized Multipole Technique) program, that is, “Max-1”(C. IIafner, Max-1, A Visual Electromagnetics Platform, Wiley,Chichester, UK, 1998). GMT is one analysis method of a Maxwell equation,wherein a scattered wave is described, while a multipole is placed as avirtual source. As regards a mask base material 102, SiN was used and,regarding a light blocking film 101, Cr was used. The pitch of the fineopening pattern was 200 nm, and the opening width was 70 nm. Theincident wavelength was 436 nm.

Numerical values (0.2, 0.4, 0.6, . . . 1.0, 1.2, and so on) in thedrawing are a relative electrical field intensity where the electricalfield intensity of the incident light is taken as 1.0.

FIG. 2 in fact illustrates an electrical field distribution peculiar tothe near field, wherein the intensity decreases as in an exponentialfunction, as coming away from the fine opening. Analyzing thisdistribution in greater detail, it has been found that the electricalfield intensity takes a peak value at an edge portion, at the lightblocking film, of the fine opening and, from there, the intensityattenuates to expand as a concentric circle. Also, it has been foundthat, even with a different opening width or opening interval or adifferent pitch pattern, simulation of an electrical field distributionto the near-field mask shows similar results, particularly when, for aperiodic pattern, the pitch of the fine opening pattern is not greaterthan the surface plasmon polariton wave, and the light blocking film ismade of a different material, that is, Au or Ta.

In the present invention, the term “opening width” refers to the widthof an opening defined by forming a light blocking film, constituting amask, where no light blocking film is present there. Specifically, inFIG. 1, for example, the portion denoted at Dmax corresponds to it.Also, the term “opening interval” refers to the distance between twoadjacent openings, that is, the width of the light blocking film there.Specifically, in FIG. 11, for example, the portion denoted at Kmincorresponds to it.

Modeling such a distribution, FIG. 3 illustrates a combined result of amodeled near-field distribution (right-hand side of FIG. 3) and thesimulation results of FIG. 2 (left-hand side of FIG. 3). In FIG. 3, forsimplicity of illustration, a portion of the field contour line shown inFIG. 2 is omitted.

It is seen from FIG. 3 that, through a concentric-circle model 600, adistribution adjacent to the light blocking film edge portion and adistribution from the edge portion to a portion 601, below the lightblocking film, are quite well approximated. Namely, theconcentric-circle model 600 depicts well the feature that the extensiondistance in the film-thickness direction (downward direction in FIG. 3)in the simulation result and the extension distance in a directionparallel to the mask surface (horizontal direction as viewed in FIG. 3)are similar to each other.

To the contrary, in this model, except the light blocking film edgeportion and the portion from the edge portion to the portion below thelight blocking film, that is, at a portion below the opening (as long asa produced pattern of exposure concerns), the electrical fielddistribution is not approximated well. Particularly, as the openingwidth becomes wider, the electrical field intensity distributiondeviates off the model. Since, however, from the simulation result,there is a tendency that the electrical field intensity below theopening increases as the opening width becomes wider, it can beconsidered that the portion below the opening is exposed constantly.Actually, in practical experiments, a result corresponding to thesimulation result was obtained at the portion below the opening.

By using this model, the structure of a near-field exposure mask to beprepared in order to obtain a desired pattern can be determined withoutthe necessity of complicated and massive simulations using variousparameters and analyses of the results. This will be described indetail, below.

Once the type of the image forming layer is fixed, the pattern to beproduced in the image forming layer can be determined by exposure amountand developing condition. Thus, when an electrical field distributionhaving a concentric extension as that of the above-described model isproduced, the pattern width thereof can have a freedom if the exposureamount and developing condition are chosen appropriately.

First of all, a case when a desired pattern to be produced is a periodicpattern will be explained. For a periodic pattern having a pitch P,also, the pitch of the mask fine opening pattern should be equal to P.For production of one having a pattern width W, from theconcentric-circle model described above, a relation of the followingequation (1) should be satisfied between the maximum value Dmax of themask opening width and the film thickness T of the image forming layer:Dmax=P−W−2×T  (1)

If the relation described with respect to D as the mask opening width isnot limited to a maximum value, it can be set forth as follows:D≦P−W−2T.

Here, T is the pattern height of the image forming layer 401 asdetermined by a subsequent process or processes.

FIG. 1 shows the relationship of values in equation (1). Thus, referringto the drawing, equation (1) will be explained in greater detail. First,the pattern height T of the image forming layer 401, by which a desiredprocessing depth of a process object substrate 402 can be processed, isdetermined on the basis of a process condition, such as etchingdurability, for example. In order to make a pattern of this height T, itis necessary that a pattern after development is produced at the fieldcontour line portion outside the field contour line 800, depicted by athick line in FIG. 1.

The electrical field distribution below the light blocking film 101 iswell approximated by a concentric-circle model 600, as describedhereinbefore. It is seen from FIG. 1 that the extension from the edgeportion of the light blocking film 1 is approximately even, both inregard to the film thickness direction (downward direction as viewed inFIG. 1) and in a direction parallel to the mask surface (horizontaldirection as viewed in FIG. 1). Therefore, if a pattern afterdevelopment is produced at the electrical field contour line 800 or anyelectrical field contour line outside the line 800, it assures a resultthat a developed pattern having an extension not less than a distance T,from the edge portion of the light blocking film 101, even in thedirection parallel to the mask surface, is produced.

The extension phenomenon from the edge portion of the light blockingfilm 101 similarly occurs at the opposite side edge of the lightblocking film 101.

Thus, the largest opening width Dmax of the near-field exposure mask,effective to produce a pattern having a pattern width W just underneaththe light blocking film 101, can be set as defined in equation (1), byusing the pattern pitch P, width W and height T.

As regards the image forming layer, any material may be used providedthat a reaction occurs in response to the near field from the openingand it can bear a process after the pattern formation. As regards theversatility, however, use of a photoresist is preferable.

The value T may be determined by a process or processes after thepattern formation and, more specifically, the etching durability in theetching process for the process object substrate, or the film thicknessof vapor deposition in the lift-off, for example.

Although it is desirable that a pattern having a thickness sufficient toprovide durability to the processing for the process object substratecan be produced only by the image forming layer, if a thickness not lessthan (P−W)/2 is necessary, a buffer layer may be prepared between theimage forming layer 401 and the process object substrate.

The buffer layer may be a resist layer, an oxide film layer, or a metallayer, for example, not processed, or, alternatively, processed so as toprovide a physical property different from the image forming layer, suchas, for example, hard baking or non-silylating in a case where a surfaceimaging method (e.g., a multilayer resist method or a surface layersilylating method), for example, is used. The buffer layer may be asingle layer or it may comprise plural layers. By transferring apattern, having been formed in the image forming layer 401 on the basisof near field exposure, to such a buffer layer in accordance with amethod such as a dry etching method, for example, one having a thicknesssufficiently durable to the processing to be made to the process objectsubstrate can be produced.

The value by which the opening width D becomes equal to Dmax is thevalue by which the process margin becomes equal to zero. In thisspecification, the term “process margin” refers to a factor that definesthe tolerance of a process with which a desired pattern height T and adesired pattern linewidth can be assuredly obtainable even taking intoaccount a process to be performed after the exposure.

The process margin “zero” means that the margin for the processcondition, such as an exposure developing condition for the patternformation or the process after the pattern formation, such as etching orvapor deposition, is zero. With such a “zero” margin, actually, it isvery difficult to perform the pattern formation and subsequent processesfor the process object substrate.

Therefore, while taking into account the process margin, the value ofthe opening width D should desirably be made smaller than Dmax, as givenby equation (2) below:D=P−W−2T(1+α)  (2)wherein α is the process margin. More specifically, it may be acomponent of an overall film thickness dissolution during thedevelopment of an image forming layer, or a component of dissolution ina direction parallel to the substrate surface during the development ofthe image forming layer, for example.

While the value α varies largely with the process, in many cases, ittakes a value of 0≦α≦4. If equation (2) takes a negative value independence upon the value of α, a buffer layer may be provided betweenthe image forming layer and the process object substrate as describedhereinbefore, to reduce the values of α and T of the effective imageforming layer, such that the opening width D having an effective andpositive value can be set.

FIG. 4 shows the relationships of these values. The reference “αp” inFIG. 4 is a value as determined by a relation 0≦αp≦α. While α is definedas the process margin, not only does it include the margin with respectto the film thickness direction, but also, it embraces the margin withrespect to a direction along the mask surface. Thus, the component αp ofmargin a only in the film thickness direction is added to the patternheight T.

A near-field exposure mask having an opening pattern pitch P and anopening width D, having been designed in the manner described above, ismanufactured, and near-field exposure and development are carried out byuse of the mask, by which a fine pattern can be produced. Details willbe described below.

FIG. 5 illustrates a general structure of a near-field exposure maskaccording to an embodiment of the present invention. The near-fieldexposure mask 1 comprises a light blocking film 101, a mask basematerial 102 and a mask supporting member 103. A thin film portion 104that presents an effectual near-field exposure mask, contributable toexposure, is defined by supporting the mask base material 102 throughthe mask supporting member 103. The light blocking film 101 may comprisea material having a low transmissivity to exposure light to be describedlater, such as Cr, Al, Au or Ta, for example.

The mask base material 102 may comprise a material having atransmissivity to exposure light to be described later, such as SiN,SiO₂, or SiC, for example, having a property different from the lightblocking film 101. There are fine openings 105 formed in the lightblocking film 101, the openings having a shape like a slit or a bore.These openings are formed in the thin film portion 104 constituted bythe light blocking film 101 and the mask base material 102 only. As willbe described later, these openings are provided so as to produce nearfield light (evanescent light) at a front surface of the mask inresponse to irradiation of the mask exposure light from the rear surfaceof the mask (upper surface thereof in FIG. 1).

The pitch and opening width of the fine opening pattern of thenear-field exposure mask are made to be equal to P and D having beendesigned as described hereinbefore.

The opening pattern may be formed by use of a processing machine, suchas an FIB, an EB, an X-ray or an SPM, or in accordance with anano-imprint method or a fine pattern forming method based on near fieldexposure.

Next, referring to FIG. 6, a method of producing a fine pattern by useof an exposure apparatus 2, which is an example for performing exposurewith use of an exposure mask 1, described above, will be explained.

FIG. 6 is a sectional view showing a general structure of an exposureapparatus 2 according to an embodiment of the present invention. Asshown in FIG. 2, the exposure apparatus 2 comprises a light source unit200, a collimator lens 300, an exposure mask 100, an exposure object 400to be exposed, and a pressure adjusting system 500.

Regarding major components of the exposure apparatus 2, the exposureapparatus 2 is arranged so that, by using the exposure mask 100 thatcorresponds to the whole surface of the exposure object 400, apredetermined pattern formed on the exposure mask 100 is transferred tothe exposure object 400 at once.

The present embodiment can be accomplished with various exposure methodssuch as, for example, a step-and-repeat exposure method wherein anexposure mask 100 smaller than an exposure object 100 is used andwherein exposure of a portion of the exposure object is carried outrepeatedly while changing the position of the exposure subject 400, or astep-and-scan exposure method.

Here, the term “step-and-scan exposure method” refers to such aprojection exposure method that an exposure mask 100 corresponding toone shot (one shot region covers one or more chip regions) is disposedopposed to one shot region of an exposure object 400, and the exposuremask 100 and the exposure object 400 are relatively and continuouslyscanned by exposure light, whereby a pattern of the exposure mask 100 islithographically transferred onto the exposure object, while on theother hand, after completion of exposure of one shot, the exposureobject 400 is moved stepwise so that a subsequent shot region of theexposure object 400 is disposed opposed to the exposure mask 100, andthen, the scanning exposure process described above is repeated.

Also, the term “step-and-repeat exposure method” refers to such aprojection exposure method that each time simultaneous exposure of oneshot of an exposure object 400 is completed, the exposure object 400 ismoved stepwise to move the same to the exposure region of a subsequentshot (i.e., the position to be opposed to the exposure mask 100), andthen, the simultaneous exposure is repeated.

In this embodiment, when the step-and-scan exposure method orstep-and-repeat exposure method is to be carried out, for every stepwisemotion, a separation operation of the mask from the exposure object 400should be done before the stepwise motion and also, anintimate-contacting operation of the mask to the exposure object 400should be done after the stepwise motion.

The light source unit 200 has a function for producing illuminationlight for illuminating the exposure mask 100 having formed thereon atransfer circuit pattern to be transferred to the substrate. As anexample, it may comprise an Hg lamp as a light source that can emitultraviolet light. However, the lamp is not limited to the Hg lamp, buta xenon lamp or a deuterium lamp, for example, may be used. Also, thereis no restriction in regard to the number of light sources.

Further, the light source to be used in the light source unit 100 is notlimited to a lamp, but one or more lasers may be used. For example, alaser that can emit ultraviolet light or soft X-rays may be used. An ArFexcimer laser having a wavelength of about 193 nm, a KrF excimer laserhaving a wavelength of about 248 nm, or an F₂ excimer laser having awavelength of about 153 nm, for example, may be used. The type of laseris not limited to an excimer laser, and a YAG laser, for example, may beused. There is no restriction in regard to the number of lasers.

The collimator lens 300 functions to transform the illumination lightemitted from the light source unit 200 into parallel light, which, inturn, is introduced into a pressurizing vessel 510 of the pressureadjusting system 500, whereby the whole surface of the exposure mask 100or only a portion thereof, which is going to be exposed, is illuminatedwith a uniform light intensity.

As has been described with reference to FIG. 5, the exposure mask 100comprises a light blocking film 101, a mask base material 102, and amask supporting member 103. From the light blocking film 101 and themask base material 102, a thin film 104 being elastically deformable isprovided. The exposure mask 100 is arranged so that a pattern as definedby the fine opening pattern 105 of the thin film 104 is transferred tothe image forming layer 401 at a unit magnification, on the basis ofnear field light. Here, the term “unit magnification” does not meanexact “1×” magnification, but it is mentioned to emphasize that themagnification differs from that in the transfer by reduction projection.

Regarding the exposure mask 100, the lower surface thereof as viewed inFIG. 6 is the front surface of the mask as being mounted. The lightblocking film 101 is disposed outside the pressurizing vessel 510 of thepressure adjusting system 500. The thin film 104 can be elasticallydeformed to assure close contact with any surface irregularities of theimage forming layer 401 or with any waviness of the exposure object 400.

The exposure object 400 comprises a process object substrate, such as awafer, for example, and an image forming layer 401 applied thereto. Theexposure object 400 is mounted on a stage 450.

As regards the image forming layer 401, use of a photoresist to be usedin ordinary photolithography is preferable. As regards the resistmaterial, use of one having a large contrast value is preferable. Thefilm thickness of the resist is T, as was described hereinbefore. Theapplication procedure for the image forming layer 401 includes apre-process, a resist coating process and a pre-baking process.

The process object substrate can be chosen from a wide variety ofmaterials, such as a semiconductor substrate (e.g., Si, GaAs or InP), aninsulative substrate (e.g., glass, quartz or BN), or one provided bysuch a substrate material and having a film of metal, oxide or nitride,for example, formed thereon. However, it should be intimately contactedto the exposure mask 100 throughout the whole exposure region with aclearance of preferably not greater than 10 nm, and at least not greaterthan 100 nm. Therefore, for the substrate 402, one having a goodflatness, as much as possible, should be chosen.

During the exposure, the image forming layer 401 and the exposure mask100 should be close to each other for execution of exposure based on thenear field light, and they are relatively approximated to each other upto a clearance of about 100 nm or less.

The stage 450 is driven by external equipment, not shown. It functionsto align the exposure object 400 relatively and two-dimensionally withrespect to the exposure mask 100, and also it operates to move theexposure object 400 upwardly and downwardly as viewed in FIG. 3.

The stage 450 of this embodiment has a function for moving the exposureobject 400 between a loading/unloading position (not shown) and theexposure position shown in FIG. 3. At the loading/unloading position, afresh exposure object 400 not having been exposed is loaded on the stage450 while, on the other hand, an exposure object 400 having been exposedis unloaded therefrom.

The pressure adjusting system 500 serves to facilitate good intimatecontact and separation between the exposure mask 100 and the exposureobject 400, more particularly, between the thin film portion 104 and theimage forming layer 401. If both of the surfaces of the exposure mask100 and the image forming layer 401 are completely flat, they can bebrought into intimate contact with each other throughout the entiresurface, by engaging them with each other. Actually, however, thesurfaces of the exposure mask 100, the image forming layer 401 andsubstrate 402 have a surface irregularity or surface waviness.Therefore, only by approximating them toward each other and bringingthem into engagement with each other, the result would be a mixeddistribution of intimate contact portions and non-intimate contactportions. In the non-intimate contact portion, the exposure mask 100 andthe exposure object 400 are not held within a range of distance throughwhich the near field light effectively functions. Therefore, it wouldresult in exposure unevenness.

In consideration of it, the exposure apparatus 2 of this embodiment isprovided with a pressure adjusting system 500, which comprises apressurizing vessel 510, a light transmission window 520 made of a glassmaterial, for example, pressure adjusting means 530, and a pressureadjusting valve 540.

The pressurizing vessel 510 can keep the gas-tightness through thecombination of the light transmission window 520, the exposure mask 100and the pressure adjusting valve 540. The pressurizing vessel 510 isconnected to the pressure adjusting means 430 through the pressureadjusting valve 540, such that the pressure inside the pressurizingvessel 510 can be adjusted. The pressure adjusting means 530 maycomprise a high-pressure gas pump, for example, and it functions toincrease the inside pressure of the pressurizing vessel 510 through thepressure adjusting valve 540.

The pressure adjusting means 530 further comprises an exhausting pump(not shown), so that it can function to decrease the inside pressure ofthe pressurizing vessel 510 through a pressure adjusting valve, notshown.

The adhesion between the thin film and the image forming layer 401 canbe adjusted by adjusting the inside pressure of the pressurizing vessel510. If the surface of the exposure mask 100, the image forming layer401 or of the substrate 402 has slightly large surface irregularities orwaviness, the inside pressure of the pressurizing vessel 510 may be setat a higher level to increase the adhesion strength, thereby, to reducedispersion of clearance between the surfaces of the mask surface 100,the image forming layer 401 and the substrate 402 due to the surfaceirregularities or waviness.

As an alternative, the front surface side of the exposure mask 100, aswell as the image forming layer 401 and the substrate 402 side, may bedisposed inside a reduced-pressure vessel 510. On that occasion, on thebasis of a pressure difference with an atmospheric pressure, higher thanthe vessel inside pressure, a pressure may be applied to the exposuremask from its rear surface side to its front surface side, whereby theadhesion between the exposure mask 100 and the image forming layer 401can be improved. Anyway, a pressure difference that the pressure at therear surface side of the exposure mask 100 is higher than the pressureat the front surface side thereof, is produced. If the surface ofexposure mask 100 or the surface of image forming layer 401 or substrate401 has slightly large surface irregularities or waviness, the pressureinside the reduced pressure vessel may be set at a lower level toincrease the adhesion, thereby to reduce dispersion of clearance betweenthe mask surface and the resist surface or substrate surface.

As a further alternative, the inside of the pressurizing vessel 510 maybe filled with a liquid, which is transparent with respect to theexposure light EL, and, by using a cylinder (not shown), the pressure ofthe liquid inside the pressurizing vessel 510 may be adjusted.

Next, the sequence of exposure using the exposure apparatus 2 will beexplained.

For exposure, the stage 450 aligns the exposure object 400 with respectto the exposure mask 100 relatively and two-dimensionally.

If the alignment is completed, the stage 450 moves the exposure object400 along a direction of a normal to the mask surface, into a rangethat, throughout the entire surface of the image forming layer 401, theclearance between the image forming layer 401 and the exposure mask 100is reduced to not greater than 100 nm, so that they can be intimatelycontacted to each other on the basis of elastic deformation of the thinfilm 104.

Subsequently, the exposure mask 100 and the exposure object 400 arebrought into intimate contact with each other. Specifically, thepressure adjusting valve 540 is opened and the pressure adjusting means530 introduces a high pressure gas into the pressurizing vessel 510,whereby the inside pressure of the pressurizing vessel 510 is raised.After this, the pressure adjusting valve 540 is closed.

As the inside pressure of the pressurizing vessel 501 increases, thethin film 104 is elastically deformed and it is pressed against theimage forming layer 401.

As a result, the thin film 104 is closely contacted to the image forminglayer 401 with uniform pressure, throughout the entire surface andwithin a range in which the near field light effectively acts on theimage forming layer. When pressure application is performed in themanner described above, in accordance with the Pascal's principle, therepulsive force acting between the thin film 104 and the image forminglayer 401 becomes uniform. This effectively avoids a phenomenon that alarge force is locally applied to the thin film 104 or the image forminglayer 401, and thus, it effectively prevents local breakage of theexposure mask 100 or the exposure object 400.

In this state, the exposure process is carried out. Namely, exposurelight is emitted from the light source unit 200 and it is transformedinto parallel light by means of the collimator lens 300. Then, theexposure light is introduced into the pressuring vessel 510 through theglass window 520. The thus introduced light passes through the exposuremask 100, disposed inside the pressurizing vessel 510 from its rearsurface side to its front surface side, that is, from the upper side tothe lower side in FIG. 3, whereby near field light leaking from thepattern defined by the fine openings of the thin film 104 is produced.

The near field light is scattered within the image forming layer 401,such that the image forming layer is exposed thereby. When the thicknessof the image forming layer 401 is sufficiently thin, the scattering ofnear field light within the image forming layer 401 does not expandlargely, such that a pattern corresponding to the fine opening, smallerthan the wavelength of exposure light, can be transferred to the imageforming layer 401.

After the exposure is completed, a valve (not shown) is opened and theinside of the pressurizing vessel 510 is evacuated through an exhaustpump (not shown) of the pressure adjusting means 530, thereby todecrease the pressure of the pressurizing vessel 510. Then, the thinfilm 104 is separated (or peeled) off from the image forming layer 401on the basis of elastic deformation.

When pressure reduction is performed in the manner described above, inaccordance with Pascal's principle, the repulsive force acting betweenthe thin film 104 and the image forming layer 401 becomes uniform. Thiseffectively avoids a phenomenon that a large force is locally applied tothe thin film 104 or the image forming layer 401, and thus, iteffectively prevents local breakage of the exposure mask 100 or theexposure object 400.

After this, the exposure object 400 is moved by the stage to theloading/unloading position where it is replaced by a fresh exposureobject 400. Subsequently, a similar procedure is repeated.

Here, the exposure amount can be set in the following manner.

The electrical field distribution, where a near field exposure maskprepared as described above, can be determined on the basis ofsimulation. Furthermore, if the relationship of the remaining filmthickness after development with respect to the exposure amount of theimage forming layer being used, namely, the solubility curve of theresist, is predetected, on the basis of it, the exposure amount and thedeveloping condition are determined so that a desired pitch P and adesired pattern width W are obtained.

More specifically, first of all, from the simulation result, theelectrical field contour line where a desired pattern width isobtainable when the intensity of incident light upon the near-fieldexposure mask is taken as one, is read out. This is denoted by “x”.Also, from the resist solubility curve, the exposure amount with whichthe standardized remaining film thickness becomes equal to 0.5 is readout. This is denoted by “I”.

As an example, FIG. 7 shows a solubility curve of a representativeresist. If a resist being used is a negative resist, the above valuetakes the same value of the sensitivity. If it is a positive resist, theabove value takes a value as designated in FIG. 7 by an inclined arrow.

If the intensity of incident light on the near-field exposure mask is J,then J and t that satisfy the relation:I=xJt  (3)are set as the intensity of incident light and the exposure time,respectively. Namely, Jt is set as the exposure amount.

As an example, a case will be explained in more detail with reference toFIG. 4.

First, an electrical field contour line 800 with which a desired patternwidth is obtainable is chosen. Regarding the contour line 800, from thesimulation result, the intensity thereof was 0.5 where the incidentintensity was taken as one. Also, from the solubility curve of a resistused, the exposure amount with which the standardized remaining filmthickness became equal to 0.5 was 220 mJ/cm². When light of 200 mW/cm²is used as the incident intensity, if follows from equation (3) that:220=0.5×200×t,such that an exposure time 1.2 sec. and an exposure amount 240 mJ/cm²are calculated.

It is sufficient that the simulation is done only in regard to anear-field exposure mask having an already determined pitch and openingwidth, that is, only with regard to one condition. Further, the numberof parameters required for conditioning the process is much reduced.Therefore, the time from a desired pattern is given, to completion ofactual manufacture, is reduced considerably.

On the other hand, in regard to a near-field mask having an alreadydetermined pitch and opening width, without simulation, the exposureamount and developing condition with which a desired pattern width W isobtainable, can be determined on the basis of a formed pattern producedwhen the exposure amount and developing condition are changed. Sincethere is no necessity of repeatedly performing complicated simulationswith various parameters, in the design of a near field exposure mask,the time required for the mask designing is reduced remarkably.

By developing the resist having a latent image formed therein in themanner described above, a fine resist pattern of a desired size can beproduced. Thereafter, an appropriate process to the substrate, such asdry etching, wet etching, or lift-off, for example, or transfer to abackground resist layer, may be carried out.

A specific example of the present invention will be explained, whilespecifying its numerical values.

As an example, a periodic slit structure having a pitch 200 nm and apattern width of 20 nm is going to be produced upon an SIO(silicon-on-insulator) wafer having an SIO layer of 100 nm thickness.Applying this to the aforementioned symbols, it follows that P=200 nmand W=20 nm.

In order that the process object substrate is an SIO layer, i.e., an Silayer, and that the Si layer is etched through a depth of 100 nm, takinginto account the margin of dry etching, the resist layer as the masklayer should have a thickness of not less than 100 nm. Thus, it followsthat:T(1+α)=100 nm.

Applying this to equation (2), the left-hand term becomes negative and,thus, a buffer layer is provided between the image forming layer and theprocess object substrate. More specifically, a dual-layer resist methodis used. A hard-baked resist layer is formed as a buffer layer upon theprocess object substrate, with a thickness of 100 nm. On this layer, aSi-containing resist is formed as an image forming layer, with athickness of 20 nm. The thickness is set so that the image forming layerfunctions as an etching mask when the image forming layer pattern istransferred to the hard-baked layer. Specifically, T=20 nm.

Regarding the process margin, when α=1.5 is chosen from its range“0≦α≦4”, from equation (2), the mask opening width D [nm] can be givenby:D=200−20−2×20×(1+1.5)=80.In consideration of this, a mask having a pitch of 200 nm and an openingwidth of 80 nm was made as a near-field exposure mask.

Using this mask, a buffer layer and an image forming layer set, as hasbeen described above, were produced on the Si layer. Through exposureand development, a pattern having a pitch of 200 nm was produced in theimage forming layer. Using this as an etching mask, an etching processwas carried out with a dry etching apparatus and an oxygen gas, a slitpattern having a pitch of 200 nm and a pattern width of 20 nm wasproduced on the buffer layer.

Further, using the pattern of the buffer layer as an etching mask, Siwas etched with a dry etching apparatus, whereby a fine Si structurehaving a pitch of 200 nm, a pattern width of 20 nm and a pattern heightof 100 nm was produced upon an insulative film.

By the way, when a mask having any one of a variety of two-dimensionallyshaped mask patterns 801, such as shown in FIGS. 9 and 10, is applied toa near-field exposure mask of the present invention such as describedhereinbefore, just underneath the mask, a latent image having atwo-dimensional shape, such as illustrated at 803, is produced. Afterexposure and development, a resist pattern 802 corresponding to it isproduced.

For example, with a mask pattern having grid-like fine openings (FIG.9A), a two-dimensional dot array (in the case of a positive typeresist), such as shown in FIG. 9A′, or a hole array (in the case of anegative type resist), is obtainable. These patterns may be suited forproduction of a two-dimensionally arrayed quantum dot array to be usedfor an optical device or an electronic device having quantum dots.

On the other hand, with a mask pattern having a two-dimensionalfine-opening array, such as shown in FIG. 9B, a two-dimensionalgrid-like array (in the case of a positive type resist), such as shownin FIG. 9B′, or a hole array (in the case of a negative type resist), isobtainable.

In the case of a mask pattern wherein a light blocking metal filmportion has a two-dimensional rectangular array, such as shown in FIG.9C, a two-dimensional fine-line pair (in the case of a positive typeresist), such as shown in FIG. 9B′, or a fine groove array (in the caseof a negative type resist), is obtainable. These patterns may be suitedfor production of a gate pattern to be used in a CMOS electronic device.

Further, in the case of a mask pattern wherein a light blocking metalfilm portion has a ring-like shape, such as shown in FIG. 10A, atwo-dimensional dot or ring array (in the case of a positive typeresist), such as shown in FIG. 10B, or a hole or ring array (in the caseof a negative type resist), is obtainable.

The foregoing description has been made with reference to a method ofproducing a pattern having a desired pitch P, a desired pattern width Wand a desired pattern height T by use of a near field exposure maskhaving an opening width D designed and manufactured as describedhereinbefore. However, on the basis of a method, such as adjusting theexposure amount, changing the resist used, changing the developingcondition, or the like, a pattern having either one or both of a patternwidth W′ and a pattern height T′ different from W and T and satisfyingthe following relation, may be manufactured:(W′+2T′)≦(P−D).  (4)

As an example, the exposure amount may be increased as compared with themethod having been described hereinbefore, or the sensitivity of aresist used may be increased, or the developing time may be increased.Any one of them or two of them may be performed and, on that occasion, apattern having a pattern width W′ satisfying a relation W′<W, even forthe same pattern height, i.e., T=T′, is obtainable.

Furthermore, a pattern having a pattern width W' satisfying a relationW′>W is obtainable when any one or two of (i) choosing the image forminglayer height satisfying T′<T and developing the exposure amount, (ii)decreasing the resist sensitivity, and (iii) shortening the developingtime are utilized.

An example will be explained in detail, with reference to FIG. 8. When adesired pattern height T′ is equal to T, an electrical field contourline 801 (depicted by a thick line in FIG. 8), which is outside theelectrical field contour line 800 (depicted by a thick line in FIG. 1),is chosen. Subsequently, the above-described exposure amount anddeveloping condition are set to assure that a pattern can be producedwith the field contour line 801. If a material used of the image forminglayer 401 is the same, by increasing the exposure amount, for example, apattern having a pattern width W′ different from W and satisfying arelation W′<W can be produced from an already prepared mask having apitch P and an opening width Dmax. Here, the values of W′ and T′ (=T)satisfy equation (4).

Subsequently, a case wherein a desired pattern to be produced is anisolated pattern, will be explained. In order to produce a patternhaving a pattern width W, from the concentric-circle model describedhereinbefore, a relation (5) below should be satisfied between a minimumvalue Kmin of the mask opening interval and the film thickness T of theimage forming layer.Kmin=W+2T  (5)

Describing it as K when the mask opening interval is not limited to aminimum value, it follows that:K≧W+2T.

FIG. 11 shows the relationship of the values in equation (5). Thus,referring to the drawing, equation (5) will be explained in more detail.

First, the pattern height T of the image forming layer 401 by which adesired processing depth of a process object substrate 402 can beprocessed, is determined on the basis of a process condition, such asetching durability, for example. In order to make a pattern of thisheight T, it is necessary that a pattern after development is producedat the field contour line portion outside the field contour line 800,depicted by a thick line in FIG. 11.

The electrical field distribution below the light blocking film 101 iswell approximated by a concentric-circle model, as describedhereinbefore. It is seen from FIG. 11 that the extension from the edgeportion of the light blocking film 101 is approximately even both inregard to the film thickness direction (downward direction as viewed inFIG. 11) and in a direction parallel to the mask surface (horizontaldirection as viewed in FIG. 11). Therefore, if a pattern afterdevelopment is produced at the electrical field contour line 800 or anyelectrical field contour line outside the line 800, it assures a resultthat a developed pattern having an extension not less than a distance T,from the edge portion of the light blocking film 101, even in thedirection parallel to the mask surface, is produced.

The extension phenomenon from the edge portion of the light blockingfilm 101 similarly occurs at the opposite side edge of the lightblocking film 101.

Thus, the minimum opening interval Kmin of the near-field exposure mask,effective to produce a pattern having a pattern width W just underneaththe light blocking film 101, can be set as defined in equation (5), byusing the pattern width W and height T.

The value by which the opening interval K becomes equal to Kmin is thevalue by which the process margin becomes equal to zero. The processmargin “zero” means that the margin for the process condition, such asan exposure developing condition for the pattern formation or theprocess after the pattern formation, such as etching or vapordeposition, is zero. With such a “zero” margin, actually, it is verydifficult to perform the pattern formation and subsequent processes forthe process object substrate.

Therefore, while taking into account the process margin, the value ofthe opening interval K should desirably be made not less than Kmin, asgiven by equation (6) below:K=W+2T(1+α)  (6)wherein α is the process margin. More specifically, it may be anincrement of a film thickness affording a margin to the etchingdurability to the etching of the substrate or a background resist, anincrement of film thickness of vapor deposition in the lift-off, acomponent of overall film thickness dissolution during the developmentof image forming layer, or a component of dissolution in a directionparallel to the substrate surface during the development of the imageforming layer, for example.

While the value α varies largely with the process, in many cases, ittakes a value of 0<α≦4. If equation (6) takes a negative value independence upon the value of α, a buffer layer may be provided betweenthe image forming layer and the process object substrate as describedhereinbefore, to reduce the values of α and T of the effective imageforming layer, such that the opening interval K, having an effective andpositive value, can be set.

A near-field exposure mask having an opening interval K, having beendesigned in the manner described above, is manufactured, and near-fieldexposure and development are carried out by use of the mask, by which anisolated fine pattern can be produced.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

1. A method of designing an exposure mask with a light blocking memberfor exposing an image forming layer provided on a substrate to nearfield light leaking from adjoining openings formed in the light blockingmember, the method comprising: determining a width D of the openings andan opening interval of the openings to be formed in the light blockingmember, wherein a relation D≦(P−W−2T) is satisfied, where T is theheight of a pattern to be produced by exposure and development prior toprocessing the substrate using the image forming layer, W is thelinewidth of the pattern to be produced by exposure and developmentprior to processing the substrate, and P is the pitch of the pattern, sothat an electrical field distribution, adjacent to the openings of thelight blocking member as exposure light is projected on the lightblocking member, is approximated to an electrical field model extendingcircularly concentric with an edge of the light blocking member at animage forming layer side as a center.
 2. An exposure method ofmanufacturing an exposure mask with a light blocking member for exposingan image forming layer provided on a substrate to near field lightleaking from adjoining openings formed in the blocking member, themethod comprising: determining a width D of the openings and an openinginterval of the openings to be formed in the light blocking member; andprocessing the light blocking member so as to obtain the width D and theopening interval, wherein a relation D≦(P−W−2T) is satisfied, where T isthe height of a pattern to be produced by exposure and development usingthe image forming layer, W is the linewidth of the pattern and P is thepitch of the pattern, so that an electrical field distribution, adjacentto the openings of the light blocking member as exposure light isprojected on the light blocking member, is approximated to an electricalfield model extending circularly concentric with an edge of the lightblocking member at an image forming layer side as a center.